High pressure apparatus and method for nitride crystal growth

ABSTRACT

A high pressure apparatus and related methods for processing supercritical fluids. In a specific embodiment, the present apparatus includes a capsule, a heater, at least one ceramic ring but can be multiple rings, optionally, with one or more scribe marks and/or cracks present. In a specific embodiment, the apparatus optionally has a metal sleeve containing each ceramic ring. The apparatus also has a high-strength enclosure, end flanges with associated insulation, and a power control system. In a specific embodiment, the apparatus is capable of accessing pressures and temperatures of 0.2-2 GPa and 400-1200° C., respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application which claims priority from U.S.application Ser. No. 12/133,364, filed Jun. 5, 2008 now U.S. Pat. No.9,097,081, entitled “High Pressure Apparatus and Method for NitrideCrystal Growth,” which application is incorporated herein by reference.In addition, this application is related to U.S. application Ser. No.13/013,697, filed Jan. 25, 2011, and entitled “Improved High PressureApparatus and Method for Nitride Crystal Growth.”

BACKGROUND OF THE INVENTION

The present invention relates generally to techniques for processingmaterials in supercritical fluids. More specifically, embodiments of theinvention include techniques for controlling parameters associated witha material processing capsule disposed within a high-pressure apparatusenclosure. Merely by way of example, the invention can be applied togrowing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and othersfor manufacture of bulk or patterned substrates. Such bulk or patternedsubstrates can be used for a variety of applications includingoptoelectronic devices, lasers, light emitting diodes, solar cells,photoelectrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors, among otherdevices.

Supercritical fluids are used to process a wide variety of materials. Asupercritical fluid is often defined as a substance beyond its criticalpoint, i.e., critical temperature and critical pressure. A criticalpoint represents the highest temperature and pressure at which thesubstance can exist as a vapor and liquid in equilibrium. In certainsupercritical fluid applications, the materials being processed areplaced inside a pressure vessel or other high pressure apparatus. Insome cases it is desirable to first place the materials inside acontainer, liner, or capsule, which in turn is placed inside the highpressure apparatus. In operation, the high pressure apparatus providesstructural support for the high pressures generated within the containeror capsule holding the materials. The container, liner, or capsuleprovides a closed/sealed environment that is chemically inert andimpermeable to solvents, solutes, and gases that may be involved in orgenerated by the process.

Scientists and engineers have been synthesizing crystalline materialsusing high pressure techniques. As an example, synthetic diamonds areoften made using high pressure and temperature conditions. Syntheticdiamonds are often used for industrial purposes but can also be grownlarge enough for jewelry and other applications. Scientists andengineers also use high pressure to synthesize complex materials such aszeolites, which can be used to filter toxins and the like. Moreover,geologists have also used high pressure techniques to simulateconditions and/or processes occurring deep within the earth's crust.High pressure techniques often rely upon supercritical fluids, hereinreferred to as SCFs.

Supercritical fluids provide an especially ideal environment for growthof high quality crystals in large volumes and low costs. In many cases,supercritical fluids possess the solvating capabilities of a liquid withthe transport characteristics of a gas. Thus, on the one hand,supercritical fluids can dissolve significant quantities of a solute forrecrystallization. On the other hand, the favorable transportcharacteristics include a high diffusion coefficient, so that solutesmay be transported rapidly through the boundary layer between the bulkof the supercritical fluid and a growing crystal, and also a lowviscosity, so that the boundary layer is very thin and small temperaturegradients can cause facile self-convection and self-stirring of thereactor. This combination of characteristics enables, for example, thegrowth of hundreds or thousands of large α-quartz crystals in a singlegrowth run in supercritical water.

Supercritical fluids also provide an attractive medium for synthesis ofexotic materials, such as zeolites, for solvent extractions, as ofcaffeine from coffee, and for decomposition and/or dissolution ofmaterials that are relatively inert under more typical conditions, suchas biofuels and toxic waste materials.

In some applications, such as crystal growth, the pressure vessel orcapsule also includes a baffle plate that separates the interior intodifferent chambers, e.g., a top half and a bottom half. The baffle platetypically has a plurality of random or regularly spaced holes to enablefluid flow and heat and mass transfer between these different chambers,which hold the different materials being processed along with asupercritical fluid. For example, in typical crystal growthapplications, one portion of the capsule contains seed crystals and theother half contains nutrient material. In addition to the materialsbeing processed, the capsule contains a solid or liquid that forms thesupercritical fluid at elevated temperatures and pressures and,typically, also a mineralizer to increase the solubility of thematerials being processed in the supercritical fluid. In otherapplications, for example, synthesis of zeolites or of nano-particles orprocessing of ceramics, no baffle plate may be used for operation. Inoperation, the capsule is heated and pressurized toward or beyond thecritical point, thereby causing the solid and/or liquid to transforminto the supercritical fluid. In some applications the fluid may remainsubcritical, that is, the pressure or temperature may be less than thecritical point. However, in all cases of interest here, the fluid issuperheated, that is, the temperature is higher than the boiling pointof the fluid at atmospheric pressure. The term “supercritical” will beused throughout to mean “superheated”, regardless of whether thepressure and temperature are greater than the critical point, which maynot be known for a particular fluid composition with dissolved solutes.

Although somewhat effective for conventional crystal growth, drawbacksexist with conventional processing vessels. As an example, processingcapabilities for conventional steel hot-wall pressure vessels (e.g.,autoclaves) are typically limited to a maximum temperature of about 400Degrees Celsius and a maximum pressure of 0.2 GigaPascals (GPa).Fabrication of conventional pressure vessels from nickel-basedsuperalloys allows for operation at a maximum temperature of about 550degrees Celsius and a maximum pressure of about 0.5 GPa. Therefore,these conventional hot-wall pressure vessels are often inadequate forsome processes, such as the growth of gallium nitride crystals insupercritical ammonia that often require pressures and temperatures thatextend significantly above this range in order to achieve growth ratesabove about 2-4 microns per hour. In addition, nickel-based superalloysare very expensive and are difficult to machine, limiting the maximumpractical size and greatly increasing the cost compared to traditionalsteel pressure vessels.

Attempts have been made to overcome the drawbacks of conventionalpressure vessels. D'Evelyn et al., US patent application 2003/0140845A1,indicates a so-called zero-stroke high pressure apparatus adapted fromthe type of belt apparatus used for synthesis of diamond using highpressure and high temperature. Cemented tungsten carbide, however, isused as the die material, which is relatively expensive and is difficultto manufacture in large dimensions. In addition, the use of a hydraulicpress to contain the apparatus increases the cost and further limits themaximum volume. Finally, the use of a pressure transmission mediumsurrounding the capsule used to contain the supercritical fluid reducesthe volume available within the hot zone for processing material.

D'Evelyn et al., US patent application 2006/0177362A1, indicates severaltypes of apparatus with capability for pressures and temperatures wellin excess of that of conventional autoclaves and with improvedscalability relative to the zero-stroke press apparatus described above.A series of wedge-shaped radial ceramic segments are placed between aheater which surrounds a capsule and a high-strength enclosure, in orderto reduce both the pressure and temperature to which the inner diameterof the high-strength enclosure is exposed compared to the correspondingvalues for the capsule. Fabrication and use of these ceramicwedge-shaped radial segments, however, can be difficult and expensive.These and other limitations of conventional apparatus may be describedthroughout the present specification.

From the above, it is seen that techniques for improving a high pressureapparatus for crystal growth is highly desirable.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, techniques related for processingmaterials in supercritical fluids are provided. More specifically,embodiments of the invention include techniques for controllingparameters associated with a material processing capsule disposed withina high-pressure apparatus/enclosure. Merely by way of example, theinvention can be applied to growing crystals of GaN, AlN, InN, InGaN,AlGaN, and AlInGaN, and others for manufacture of bulk or patternedsubstrates. Such bulk or patterned substrates can be used for a varietyof applications including optoelectronic devices, lasers, light emittingdiodes, solar cells, photo electrochemical water splitting and hydrogengeneration, photodetectors, integrated circuits, and transistors, andothers.

In a specific embodiment, the present invention provides a high pressureapparatus and related methods for processing supercritical fluids. In aspecific embodiment, the present apparatus includes a capsule, a heater,at least one ceramic ring but can be multiple rings, optionally, withone or more scribe marks and/or cracks present. In a specificembodiment, the apparatus optionally has a metal sleeve containing eachceramic ring. The apparatus also has a high-strength enclosure, endflanges with associated insulation, and a power control system. Theapparatus is scalable up to very large volumes and is cost effective. Ina specific embodiment, the apparatus is capable of accessing pressuresand temperatures of 0.2-2 GPa and 400-1200° C., respectively. As usedherein in a specific embodiment, the term “high-strength” generallymeans suitable mechanical and other features (e.g., tensile strength,Young's Modulus, yield strength, toughness, creep resistance, chemicalresistance) that allow for use as a high pressure enclosure, such as apressure vessel, which may be airtight, but may also not be air and/orgas tight). As an example, the term “high pressure” generally refers toabove 0.1 GPa, 0.2 GPa, 0.5 GPa, and others, particularly in pressuressuitable for growth of crystalline materials, including but not limitedto GaN, AlN, InN, AlGaN, InGaN, AlInGaN, and other nitrides or oxides ormetal or dielectric or semiconducting materials. In a specificembodiment, the high strength enclosure material is provided to form ahigh strength enclosure configured to withstand a load of greater thanabout 0.1 GPa (or 0.2 GPa or 0.5 GPa) for a predetermined time period ata temperature of about 200 Degrees Celsius or less.

In an alternative specific embodiment, the present invention providesapparatus for high pressure crystal or material processing, e.g., GaN,AlN, InN, InGaN, AlGaN, and AlInGaN. The apparatus includes acylindrical capsule region comprising a first region and a secondregion, and a length defined between the first region and the secondregion. The apparatus has an annular heating member enclosing thecylindrical capsule region. The apparatus has at least one continuousannular ceramic (or metal or cermet) member having a predeterminedthickness disposed continuously around a perimeter of the annularheating member. In a specific embodiment, the continuous annular memberis made of a material having a compressive strength of about 0.5 GPa andgreater and a thermal conductivity of about 4 watts per meter-Kelvin andless. In a specific embodiment, the apparatus has a high strengthenclosure material disposed overlying the annular ceramic member.

Still further, the present invention provides a method of crystalgrowth, e.g., GaN, AlN, InN, InGaN, AlGaN, and AlInGaN. The methodincludes providing an apparatus for high pressure crystal growth ormaterial processing. The apparatus includes a cylindrical capsule regioncomprising a first region and a second region, and a length definedbetween the first region and the second region. The apparatus also hasan annular heating member enclosing the cylindrical capsule region. Theapparatus has at least one continuous ceramic or annular metal or cermetmember having a predetermined thickness disposed continuously around aperimeter of the annular heating member. In a preferred embodiment, thecontinuous annular member is made of a material having a compressivestrength of about 0.5 GPa and greater and a thermal conductivity ofabout 4 watts per meter-Kelvin and less. The apparatus also has a highstrength enclosure material disposed overlying the annular ceramicmember. In a specific embodiment, the method also includes providing acapsule containing a solvent and placing the capsule within an interiorregion of the cylindrical capsule region. In a specific embodiment, themethod includes processing the capsule with thermal energy to cause anincrease in temperature within the capsule to greater than 200 DegreesCelsius to cause the solvent to be superheated.

Moreover, depending upon the embodiment, the present method can alsoincludes one of a plurality of optional steps. Optionally, the methodincludes forming a crystalline material from a process of thesuperheated solvent. Additionally, the method includes removing thermalenergy from the capsule to cause a temperature of the capsule to changefrom a first temperature to a second temperature, which is lower thanthe first temperature. The method also includes removing a first flangeand a second flange from the high pressure apparatus and moving amechanical member, using a hydraulic drive force, from the first regionof the cylindrical capsule region toward the second region to transferthe capsule out of the cylindrical capsule region. In a preferredembodiment, the present apparatus can be scaled up in size to a capsulevolume of 0.3 liters, to about 300 liters and greater.

Benefits are achieved over pre-existing techniques using the presentinvention. In particular, the present invention enables a cost-effectivehigh pressure apparatus for growth of crystals such as GaN, AlN, InN,InGaN, and AlInGaN and others. In a specific embodiment, the presentmethod and apparatus can operate with components that are relativelysimple and cost effective to manufacture, such as ceramic and steeltubes. A specific embodiment also takes advantage of the one or morecracks provided in the ceramic member, which insulates the heater.Depending upon the embodiment, the present apparatus and method can bemanufactured using conventional materials and/or methods according toone of ordinary skill in the art. The present apparatus and methodenable cost-effective crystal growth and materials processing underextreme pressure and temperature conditions in batch volumes larger than0.3 liters, larger than 1 liter, larger than 3 liters, larger than 10liters, larger than 30 liters, larger than 100 liters, and larger than300 liters according to a specific embodiment. Depending upon theembodiment, one or more of these benefits may be achieved. These andother benefits may be described throughout the present specification andmore particularly below.

The present invention achieves these benefits and others in the contextof known process technology. However, a further understanding of thenature and advantages of the present invention may be realized byreference to the latter portions of the specification and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a conventional apparatus.

FIG. 2 is a simplified diagram of a high pressure apparatus according toan embodiment of the present invention.

FIG. 3 is a simplified diagram of a cross-sectional view diagram of ahigh pressure apparatus according to an embodiment of the presentinvention.

FIG. 4 is a simplified diagram of a cross-sectional view diagram of ahigh pressure apparatus according to an embodiment of the presentinvention.

FIG. 5 is a simplified flow diagram of a method of processing a materialwithin a supercritical fluid according to an embodiment of the presentinvention.

FIG. 6 is a simplified flow diagram of an alternative method ofprocessing a material within a supercritical fluid according to analternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, techniques for processing materialsin supercritical fluids are included. More specifically, embodiments ofthe invention include techniques for controlling parameters associatedwith a material processing capsule disposed within a high-pressureapparatus/enclosure. Merely by way of example, the invention can beapplied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaNfor manufacture of bulk or patterned substrates. Such bulk or patternedsubstrates can be used for a variety of applications includingoptoelectronic devices, lasers, light emitting diodes, solar cells,photo electrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors.

In a specific embodiment, the present invention provides a high pressureapparatus for processing materials. Depending upon the embodiment, theapparatus has been described with reference to a specific orientationrelative to the direction of gravity. As an example, the apparatus isdescribed as being vertically oriented. In another embodiment, theapparatus is instead horizontally oriented or oriented at an obliqueangle intermediate between vertical and horizontal, and may be rocked soas to facilitate convection of the supercritical fluid within thecapsule.

To provide a point of reference, the force-wedge apparatus described byD'Evelyn et al. in U.S. Patent Application No. 2006/0177362A1, which isincorporated by reference in its entirety herein, is shown in FIG. 1. Acapsule, such as described in U.S. Pat. No. 7,125,453, is placed withina heater, such as that described in U.S. Patent Application No.2008/0083741A1, each of which is incorporated by reference herein. Bothare contained within a high-strength enclosure, which may be fabricatedfrom SA 723 pressure vessel steel. Then from paragraph 51, “The process. . . includes disposing a plurality of radial segments between the highstrength enclosure and the capsule (block 126). These radial segmentsare disposed one after another around a circumference of the capsule,such that each radial segment is a wedge-shaped portion of a segmentedcylinder. The radial segment may comprise a ceramic, such as alumina,silicon nitride, silicon carbide, zirconia, or the like. The radialsegment may alternatively comprise a refractory metal, such as tungsten,molybdenum, or TZM alloy, or a cermet, such as Co-cemented tungstencarbide.” As noted, limitations exist with the conventional force wedgeapparatus. That is, I later discovered that each of the radial segmentsis difficult to fabricate accurately and also difficult to assemble intothe apparatus.

FIG. 2 is a simplified diagram of a high pressure apparatus according toan embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims herein.One of ordinary skill in the art would recognize other variations,modifications, and alternatives. As shown, the present inventionprovides an apparatus for high pressure crystal or material processing,e.g., GaN, AlN, InN, InGaN, AlGaN, and AlInGaN. Other processing methodsinclude hydrothermal crystal growth of oxides and other crystallinematerials, hydrothermal or ammonothermal syntheses, and hydrothermaldecomposition, and others.

Referring to FIG. 2, high pressure apparatus 200 and related methods forprocessing supercritical fluids are disclosed. In a specific embodiment,the present apparatus 200 includes a capsule 210, a heating member orheater 212, at least one ceramic ring 214 but can be multiple rings,optionally, with one or more scribe marks and/or cracks present. In aspecific embodiment, the apparatus optionally has one or more metalsleeves (not shown) containing each ceramic ring. The apparatus also hasa high-strength enclosure 218, end flanges 226, 228 with associatedinsulation, and a power control system 230. The apparatus is scalable upto very large volumes and is cost effective. In a specific embodiment,the apparatus is capable of accessing pressures and temperatures of0.2-2 GPa and 400-1200° C., respectively. In a specific embodiment, theapparatus also includes a temperature controller 232.

In a specific embodiment, apparatus 200 comprises at least one heat zoneand optionally more, such as multiple, including two or more. The heatzones include an uppermost first zone 220, a growth zone 222, a bafflezone 224, and a charge or nutrient zone 226 according to a specificembodiment. When a capsule is inserted into the volume defined by aheater inner surface, an internal baffle (not shown) aligns with thebaffle gap zone according to a specific embodiment. The baffle definestwo chambers inside the capsule, one for nutrient and one for growthaccording to a specific embodiment. The two chambers communicate throughthe perforated baffle, which can have various shapes and configurations.In the illustrated embodiment, appropriate for crystal growth when thesolubility of the material to be recrystallized is an increasingfunction of temperature, the growth zone is located above the nutrientzone. In other embodiments, appropriate for crystal growth when thesolubility of the material to be recrystallized is a decreasing functionof temperature, i.e., retrograde solubility, the growth zone is locatedbelow the nutrient zone. In still other embodiments, apparatus 200 isapproximately horizontal rather than vertical and may be fitted with arocking mechanism (not shown).

In an embodiment, the capsule suitable for insertion inside the heateris formed from a precious metal. Examples of precious metals includeplatinum, palladium, rhodium, gold, or silver. Other metals can includetitanium, rhenium, copper, stainless steel, zirconium, tantalum, alloysthereof, and the like. In an embodiment, the metal functions as anoxygen getter. Suitable capsule dimensions may be greater than 2 cm indiameter and 4 cm in length. In one embodiment, the dimension of thediameter is in a range selected from any of: 2-4 cm, 4-8 cm, 8-12 cm,12-16 cm, 16-20 cm, 20-24 cm, and greater than 24 cm. In a secondembodiment, the ratio of the length to diameter of the capsule isgreater than 2. In yet another embodiment, the ratio of length todiameter is in a range of any of: 2 to 4, 4 to 6, 6 to 8, 8 to 9, 9 to10, 10 to 11, 11 to 12, 12 to 14, 14 to 16, 16 to 18, 18 to 20, andgreater than 20.

In an embodiment, the growth zone 222 volume has twice the charge zone226 volume. The electrical circuits for each heating element segment areindependently controlled. Independent control provides flexibility toachieve and maintain a heat deposition profile along the capsule height.A physical discontinuity between the second and third heater segments,from the top, produces a local dip in temperature near a baffle platedisposed in the capsule and separating the charge zone 226 from thegrowth zone 222. In an embodiment, the charge zone and the growth zoneare isotherms at temperatures that differ from each other. The bafflezone has a temperature gradient over a relatively small distance betweenthe charge zone and the growth zone isotherms. The winding patterns ofthe heating elements, and the resultant isotherms with minimaltemperature gradient spacing therebetween minimize or eliminate wallnucleation inside the capsule and in or on the baffle. In an embodiment,the growth zone may be at the bottom and the charge zone at the top.Such configurations may be based on specific chemistries and growthparameters.

With particular reference to FIG. 2, the heater 212 is disposed in anapparatus 200 that includes a vessel or high strength enclosure 218.Attachable to the top end of the vessel is first end flange 228, and tothe bottom end is a second end flange 226. A plurality of fasteners 216(only one of which is indicated with a reference number) secure the endflanges to the vessel ends.

Within the vessel 218, continuous annular ceramic member 214 lines thevessel inner surface and contacts the outer surface of the heater 212.Examples of annulus materials include but are not limited to zirconiumoxide or zirconia. First and second end caps 232 (only one of which isshown) are located proximate to the ends of the heater 212 inside thevessel. An annular plug 234 is shown as stacked disks, but may be anannulus surrounding the cap 232. The plug 234 optionally can be disposedon at least one end and within a cavity between the capsule and the endflange to reduce axial heat loss and may comprise zirconium oxide orzirconia. Alternative plug materials may include magnesium oxide, salts,and phyllosilicate minerals such as aluminum silicate hydroxide orpyrophyllite according to a specific embodiment.

Apparatus 200 may include a pressure transmission medium between theaxial ends (See reference numeral 106) of the capsule and the end capsand/or annular plugs according to a specific embodiment. The pressuretransmission medium may comprise sodium chloride, other salts, orphyllosilicate minerals such as aluminum silicate hydroxide orpyrophyllite or other materials according to a specific embodiment.However, notwithstanding the optional presence of a coating or foil todecrease friction and promote the sliding removal of the capsule afteroperation, the interface between the outer diameter of the capsule andthe inner diameter of the heating member may be substantially free ofpressure transmission medium. In addition, the interface between theouter diameter of the heating member and the inner diameter of thecontinuous annular ring is substantially free of pressure transmissionmedium.

The illustrated apparatus 200 can be used to grow crystals underpressure and temperature conditions desirable for crystal growth, e.g.,gallium nitride crystals under related process conditions. Thehigh-pressure apparatus 200 can include one or more structures operableto support the heater 212 radially, axially, or both radially andaxially. The support structure in one embodiment thermally insulates theapparatus 200 from the ambient environment, and such insulation mayenhance or improve process stability, maintain and control a desiredtemperature profile.

In a specific embodiment, the apparatus includes a cylindrical capsuleregion comprising a first region and a second region, and a lengthdefined between the first region and the second region. In a specificembodiment, a capsule is disposed within the cylindrical capsule region.As an example, the capsule is made of a suitable material that ischemically inert, can withstand pressure, and may also be easy tohandle, among other features. Depending upon the embodiment, the capsuleis made of a material selected from gold, platinum, silver, orpalladium. Of course, there can also be other suitable materials, whichcan also include alloys, coatings, and/or multi-layered structures,depending upon the specific embodiment. Other metals can includetitanium, rhenium, copper, stainless steel, zirconium, tantalum, alloysthereof, and the like. In a specific embodiment, the capsule ischaracterized by a deformable material and is substantially chemicallyinert relative to one or more reactants within the cylindrical capsuleregion. An example of a capsule is described in U.S. Pat. No. 7,125,453,which is incorporated by reference herein for all purposes.

In a specific embodiment, the apparatus has an annular heating memberenclosing the cylindrical capsule region. Another example of a heatingmember is described in U.S. Patent Application No. 2008/0083741A1, whichis also incorporated by reference herein. The heating member may have atleast two independently controllable hot zones and may be capable ofgenerating heating power as large as 3 kilowatts, 10 kilowatts, 30kilowatts, 100 kilowatts, 300 kilowatts, or 1000 kilowatts.

In a specific embodiment, the apparatus has at least one continuousannular ceramic or metal or cermet member having a predeterminedthickness disposed continuously around a perimeter of the annularheating member. In a specific embodiment, the continuous annular memberis made of a material having a compressive strength of about 0.5 GPa andgreater and a thermal conductivity of about 4 watts per meter-Kelvin andless. As an example, the ceramic material can comprise rare earth metaloxide, zirconium oxide, hafnium oxide, magnesium oxide, calcium oxide,aluminum oxide, yttrium oxide, sialon (Si—Al—O—N), silicon nitride,silicon oxynitride, garnets, cristobalite, and mullite. The ceramicmaterial may be a composite, comprising more than one phase.Alternatively, as an example, the metal can be a refractory metal suchas tungsten, molybdenum, TZM alloy, and others. The cermet can becobalt-cemented tungsten carbide, and others. In an alternativeembodiment, which will be described further below, the continuousannular ceramic, metal, or cermet member is configured to include aplurality of crack regions disposed in a non-symmetrical manner anddisposed between an inner diameter of the continuous annular ceramic,metal, or cermet member and an outer diameter of the continuous annularceramic, metal, or cermet member. In a specific embodiment, the annularmember is one of a plurality of members, which are stacked on top ofeach other.

In a specific embodiment, the apparatus also has a cylindrical sleevemember disposed overlying the at least annular ceramic, metal or cermetmember. As an example, the cylindrical sleeve member is made of amaterial selected from stainless steel, iron, steel, iron alloy, nickelor nickel alloy, or any combinations thereof. In a specific embodiment,the cylindrical sleeve member comprises a first end and a second end. Ina specific embodiment, the cylindrical sleeve has determined dimensions.

Depending upon the embodiment, the first end is characterized by a firstouter diameter and the second end is characterized by a second outerdiameter, which is less than the first outer diameter, to form a taperangle between an axis of the cylindrical sleeve member and an outerregion of the cylindrical sleeve member, the taper angle ranging fromabout 0.1 to 5 Degrees.

Additionally, the cylindrical sleeve member comprises a substantiallyconstant inner diameter from the first end to the second end accordingto a specific embodiment, although the inner diameter can also varydepending upon the embodiment. In a preferred embodiment, thecylindrical sleeve member is configured to compress the continuousannular ceramic member in cooperation with the high pressure enclosurematerial. In a preferred embodiment, the cylindrical sleeve member isconfigured to provide mechanical support to maintain a determined shapeof the continuous annular ceramic member. In a more preferredembodiment, the cylindrical sleeve is configured to compress thecontinuous annular ceramic member in cooperation with the high pressureenclosure material and is configured to provide mechanical support tomaintain a determined shape of the continuous annular ceramic member.

In a specific embodiment, the apparatus has an high strength enclosurematerial disposed overlying the annular ceramic member. In a specificembodiment, the high strength enclosure is made of a suitable materialto house internal contents including capsule, heater, sleeve, amongother elements. In a specific embodiment, the high strength enclosure ismade of a material selected from a group consisting of steel, low-carbonsteel, SA723 steel, SA266 carbon steel, 4340 steel, A-286 steel, ironbased superalloy, 304 stainless steel, 310 stainless steel, 316stainless steel, 340 stainless steel, 410 stainless steel, 17-4precipitation hardened stainless steel, zirconium and its alloys,titanium and its alloys, and other materials commonly known as Monel,Inconel, Hastelloy, Udimet 500, Stellite, Rene 41, and Rene 88. In apreferred embodiment, the high strength enclosure comprises a materialwith ultimate tensile strength and yield strength characteristics so asto be rated by the American Society of Mechanical Engineers forcontinuous operation as a pressure vessel at a pressure higher than50,000 pounds per square inch.

The high strength enclosure also has a desired length and widthaccording to a specific embodiment. In a specific embodiment, the highstrength enclosure has a length and an inner diameter to define anaspect ratio between about 2 to about 25. The high strength enclosurehas a length and an inner diameter to define an aspect ratio of aboutten to about twelve. In a specific embodiment, the inner diameter isbetween about two inches and about fifty inches. In a specificembodiment, the height of the high strength enclosure is between 6inches and 500 inches. The ratio between the outer diameter and theinner diameter of the high strength enclosure may be between 1.2 and 5.In a specific embodiment, the diameter ratio may be between about 1.5and about 3.

In a specific embodiment, the present apparatus 300 is illustrated byway of FIG. 3. This diagram is merely an example, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art would recognize other variations, modifications, andalternatives. Instead of individual radial segments disposed one afteranother within the apparatus, one or more rings 307 may be stackedwithin the apparatus. The ring may comprise a ceramic, such as alumina,silicon nitride, silicon carbide, zirconia, or the like, including othermaterials described herein as well as outside of the specification,which are known to one of ordinary skill in the art. The ring mayalternatively comprise a refractory metal, such as tungsten, molybdenum,or TZM alloy, or a cermet, such as Co-cemented tungsten carbide. Thering may have an inner diameter between 0.5 inch and 24 inches, an outerdiameter between 1 inch and 48 inches, and a height between 1 inch and96 inches. In a specific embodiment, the inner diameter is between about1.5 inches and about 8 inches and the height is between 1.5 inches and 8inches. The ratio between the outer diameter and the inner diameter ofthe rings may be between 1.05 and 60. In a specific embodiment, thediameter ratio may be between about 1.5 and about 3. The ring may have adensity greater than 95% of theoretical density. The modulus of ruptureof the ring material may be greater than 200 or 450 MPa. The fracturetoughness of the ring material may be greater than 9 MPa-m^(1/2).Depending on the dimensions of the rings and of the high-strengthenclosure, one to 200 rings may be stacked on top of one another insidethe high-strength enclosure.

In a specific embodiment, a spacer, with a thickness between 0.001 inchand 0.1 inch, may be placed between successive rings in the stack toallow for thermal expansion. A sleeve 309 may be placed around eachring. The sleeve may comprise steel or other suitable material accordingto a specific embodiment. The sleeve may be between 0.020 inch and 0.5inch thick, and their height may be between 0.25 inch less than that ofthe ring and 0.1 inch greater than that of the ring depending upon theembodiment. The apparatus also includes a capsule 301, thermocouples303, which are coupled electrically to temperature controller and/orpower controller, a heater 305, a high strength enclosure 311, amongother elements.

In a specific embodiment the ceramic rings do not crack significantlyunder operating conditions, as represented in FIG. 3. The fracturestrength of the rings may be higher than the operating pressure of thecapsule, for example. In another embodiment, radial compressive loadingof the rings is provided by an interference fit with the high strengthenclosure. In an embodiment, an interference fit is achieved by at leastone of heating of the high strength enclosure and cooling of the ringprior to assembly. In another embodiment, an interference fit isachieved by grinding a slight taper, for example, approximately onedegree, on the inner diameter of the high strength enclosure and on thering and/or the sleeve surrounding the ring, and then pressing the ringand sleeve into the high strength enclosure to achieve the interferencefit.

In another embodiment, the rings have at least one crack under operatingconditions in the apparatus 400, as shown in FIG. 4. In a specificembodiment, the rings 407 are inserted into the high strength enclosureand allowed to crack during initial operation. Cracking in particularpositions may be facilitated by scribing the inner diameter of the ringat the points of the desired crack initiation. The resulting cracks mayrun all the way from the inner diameter to the outer diameter, or theymay terminate within the volume of the ring and/or have any combinationsof these structures. In another embodiment, the rings are cracked priorto insertion into the high strength enclosure. Pre-cracking may beachieved by sliding a precision-turned rod having a larger coefficientof thermal expansion than the ring into the inner diameter of the ringand heating. The sleeve 409 surrounding the ring will keep and maintainall parts of the ring together and precisely oriented with respect toeach other in the event that cracks run completely through the ring atvarious radial positions. In another embodiment, cracks are presentwithin the volume of the ring and contact neither the inner diameter northe outer diameter of the ring. The apparatus 400 also includes acapsule 401, thermocouples 403, which are coupled electrically totemperature controller and/or power controller, a heater 405, a highstrength enclosure 411, among other elements.

The vertical dimension runs out of the page in FIGS. 3 and 4. The topand bottom of the cavity defined by the inner diameter of the rings isterminated by insulating plugs positioned proximate to end flanges, asshown in FIG. 2. The end flanges may be attached to the high strengthenclosure by means of bolts. The length-to-diameter ratio of the cavityshould be at least 2:1 and more preferably lies in the range between 5:1and 15:1.

In order to measure the temperature at various heights on the outerdiameter of the capsule, prior to assembly at least one axial dent orgroove is placed on the outer diameter of the capsule at specifiedradial positions. In the examples shown in FIGS. 3 and 4, four dents orgrooves are placed 90 degrees apart along the outer diameter of thecapsule. The groove or dent may extend the entire height of the capsuleor may terminate at the height along the capsule where a temperaturemeasurement is desired. The width and depth of the groove or dent may bebetween about 0.025 inch and 0.130 inch. Holes slightly larger indiameter than the thermocouple may be placed in one or both end flanges.Holes or grooves may also be placed in at least one insulating cylinderseparating the end flange from the capsule. Thermocouples may beinserted into the grooves or dents after insertion of the capsule intothe heater, followed by placement of the end flanges onto the highstrength enclosure. Alternatively, one or more thermocouples may beinserted into the grooves or dents prior to placement of the endflanges, and the free ends strung through the end flanges prior toplacement of the latter and attachment of the electrical connections tothe free ends of the thermocouples.

A method according to a specific embodiment is briefly outlined below.

1. Provide an apparatus for high pressure crystal growth or materialprocessing, such as the one described above, but can be others, theapparatus comprising a cylindrical capsule region comprising a firstregion and a second region, and a length defined between the firstregion and the second region, an annular heating member enclosing thecylindrical capsule region, at least one continuous ceramic or annularmetal or cermet member having a predetermined thickness disposedcontinuously around a perimeter of the annular heating member and anhigh strength enclosure material disposed overlying the annular ceramicmember;

2. Provide capsule containing a solvent;

3. Place the capsule within an interior region of the cylindricalcapsule region;

4. Process the capsule with thermal energy to cause an increase intemperature within the capsule to greater than 200 Degrees Celsius tocause the solvent to be superheated;

5. Form a crystalline material from a process of the superheatedsolvent;

6. Remove thermal energy from the capsule to cause a temperature of thecapsule to change from a first temperature to a second temperature,which is lower than the first temperature;

7. Remove a first flange and a second flange from the high pressureapparatus;

8. Move a mechanical member, using a hydraulic drive force, from thefirst region of the cylindrical capsule region toward the second regionto transfer the capsule out of the cylindrical capsule region;

9. Open the capsule;

10. Remove the crystalline material; and

11. Perform other steps, as desired.

FIG. 5 is a simplified diagram 500 of a method of processing asupercritical fluid according to an embodiment of the present invention.In a specific embodiment, the method beings with start, step 501. Themethod begins by providing (step 503) an apparatus for high pressurecrystal or material processing, such as the one described above, but canbe others. In a specific embodiment, the apparatus has a cylindricalcapsule region comprising a first region and a second region, and alength defined between the first region and the second region. Theapparatus also has an annular heating member enclosing the cylindricalcapsule region, at least one continuous ceramic or annular metal orcermet member having a predetermined thickness disposed continuouslyaround a perimeter of the annular heating member and a high strengthenclosure material disposed overlying the annular ceramic member.

In a specific embodiment, the method provides (step 505) a capsulecontaining a solvent, such as ammonia, for example. In a specificembodiment, the method places (step 507) the capsule containing thesolvent and starting crystal within an interior region of thecylindrical capsule region. The method processes (step 509) the capsulewith thermal energy to cause an increase in temperature within thecapsule to greater than 200 Degrees Celsius to cause the solvent to besuperheated.

Referring again to FIG. 5, the method forms (step 511) a crystallinematerial from a process of the superheated solvent. In a preferredembodiment, the crystalline material is gallium containing crystal suchas GaN, AlGaN, InGaN, and others. In a specific embodiment, the methodremoves (step 513) thermal energy from the capsule to cause atemperature of the capsule to change from a first temperature to asecond temperature, which is lower than the first temperature. Once theenergy has been removed and temperature reduced to a suitable level, themethod removes one or more flanges (step 515), which mechanically heldat least the capsule in place. In a preferred embodiment, the methoduses a mechanical member, such as a plunger, to hydraulically move (step517) the mechanical member from the first region of the cylindricalcapsule region toward the second region to transfer the capsule out ofthe cylindrical capsule region free from the apparatus.

In a specific embodiment, the capsule is now free from the apparatus. Ina specific embodiment, the capsule is opened, step 519. In a preferredembodiment, the crystalline material is removed from an interior regionof the capsule, step 521. Depending upon the embodiment, there can alsobe other steps, which can be inserted or added or certain steps can alsobe removed. In a specific embodiment, the method ends at stop, step 523.

A method according to an alternative specific embodiment is brieflyoutlined below.

1. Assemble an apparatus for high pressure crystal or materialprocessing, such as the one described above, but can be others, theapparatus comprising a cylindrical capsule region comprising a firstregion and a second region, and a length defined between the firstregion and the second region, an annular heating member enclosing thecylindrical capsule region, at least one continuous ceramic or annularmetal or cermet member having a predetermined thickness disposedcontinuously around a perimeter of the annular heating member and anhigh strength enclosure material disposed overlying the annular ceramicmember;

2. Provide material to be processed and solvent in a capsule;

3. Place the capsule within an interior region of the cylindricalcapsule region;

4. Place annular plugs, end caps, end flanges onto ends of theapparatus;

5. Attach end flanges using at least one fastener;

6. Provide electrical energy to heating member to cause an increase intemperature within the capsule to greater than 200 Degrees Celsius tocause the solvent to be superheated;

7. Form a crystalline material from a process of the superheatedsolvent;

8. Remove thermal energy from the capsule to cause a temperature of thecapsule to change from a first temperature to a second temperature,which is lower than the first temperature;

9. Remove a first flange and a second flange from the high pressureapparatus;

10. Move a mechanical member, using a hydraulic drive force, from thefirst region of the cylindrical capsule region toward the second regionto transfer the capsule out of the cylindrical capsule region;

11. Open the capsule;

12. Remove the crystalline material; and

13. Perform other steps, as desired.

FIG. 6 is a simplified flow diagram 600 of an alternative method ofprocessing a material within a supercritical fluid according to analternative embodiment of the present invention. In a specificembodiment, the method beings with start, step 601. The method begins byassembling (step 603) an apparatus for high pressure crystal or materialprocessing, such as the one described above, but can be others. In aspecific embodiment, the apparatus has a cylindrical capsule regioncomprising a first region and a second region, and a length definedbetween the first region and the second region. The apparatus also hasan annular heating member enclosing the cylindrical capsule region andat least one continuous ceramic or annular metal or cermet member havinga predetermined thickness disposed continuously around a perimeter ofthe annular heating member, which are assembled together, step 605. In aspecific embodiment, the capsule, heating member, and annular member areinserted into a high strength enclosure material disposed overlying theannular ceramic member.

In a specific embodiment, the method provides a capsule containing asolvent, such as ammonia, for example, which includes a material to beprocessed, step 607. In a preferred embodiment, the capsule is sealed,step 609. In a specific embodiment, each of the capsule ends are weldedand/or brazed to form a sealed capsule structure. In a specificembodiment, the method assembles by placing (step 611) the capsulecontaining the solvent and starting crystal within an interior region ofthe cylindrical capsule region. In a preferred embodiment, the methodplaces annular plugs, end caps, and end flanges on to each of the endsof the apparatus, step 613. See, for example, FIG. 2. In a preferredembodiment, each of the end flanges is secured by way of a fastener or aplurality of fasteners.

In a specific embodiment, the method provides electrical energy (step617) in the form of power to the heating member. The heating memberprovides thermal energy to the capsule to a predetermined processtemperature and pressure, which cause the solvent to be in asupercritical state according to a specific embodiment. The methodprocesses the capsule with thermal energy to cause an increase intemperature within the capsule to greater than 200 Degrees Celsius tocause the solvent to be superheated.

In a specific embodiment, the method forms a crystalline material from aprocess of the superheated solvent. In a preferred embodiment, thecrystalline material is gallium containing crystal such as GaN, AlGaN,InGaN, and others. In a specific embodiment, the method removes thermalenergy from the capsule to cause a temperature of the capsule to changefrom a first temperature to a second temperature, which is lower thanthe first temperature. Once the energy has been removed and temperaturereduced to a suitable level, the method removes one or more flanges,which mechanically held at least the capsule in place. In a preferredembodiment, the method uses a mechanical member, such as a plunger, tohydraulically move the mechanical member from the first region of thecylindrical capsule region toward the second region to transfer thecapsule out of the cylindrical capsule region free from the apparatus.

In a specific embodiment, the capsule is now free from the apparatus. Ina specific embodiment, the capsule is opened. In a preferred embodiment,the crystalline material is removed from an interior region of thecapsule. Depending upon the embodiment, there can also be other steps,which can be inserted or added or certain steps can also be removed. Ina specific embodiment, the method ends at stop, step 619.

The above sequence of steps provides a method according to an embodimentof the present invention. In a specific embodiment, the presentinvention provides a method and resulting crystalline material providedby a high pressure apparatus having structured support members. Otheralternatives can also be provided where steps are added, one or moresteps are removed, or one or more steps are provided in a differentsequence without departing from the scope of the claims herein.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. An apparatus for crystal growth comprising: acylindrical capsule region for containing a cylindrical capsule withinwhich a crystal is to be grown under elevated pressure and temperature,the cylindrical capsule region having a length and ends; an annularheating member enclosing the length of the cylindrical capsule regionfor heating the contents of the cylindrical capsule to an elevatedtemperature to create an elevated pressure within the capsule; at leastone annular ceramic member disposed around the annular heating member,wherein the at least one annular ceramic member comprises one or more ofa rare earth metal oxide, zirconium oxide, hafnium oxide, magnesiumoxide, calcium oxide, aluminum oxide, yttrium oxide, sialon (Si—Al—O—N),silicon nitride, silicon oxynitride, garnets, cristobalite, and mullite;and an enclosure disposed around all of the at least one annular ceramicmembers.
 2. Apparatus as in claim 1 wherein the annular heating memberis substantially rigid.
 3. Apparatus as in claim 1 wherein the annularheating member is disposed in contact with the cylindrical capsule. 4.Apparatus as in claim 1 wherein the annular heating member is disposedin contact with the at least one annular ceramic member.
 5. Apparatus asin claim 1 further comprising a cylindrical sleeve surrounding at leastone annular ceramic member.
 6. Apparatus as in claim 5 wherein thecylindrical sleeve applies compressive force to the at least one annularceramic member.
 7. Apparatus as in claim 5 wherein the cylindricalsleeve comprises a material selected from steel, iron, nickel, andalloys thereof.
 8. Apparatus as in claim 1 wherein the enclosurecomprises a material selected from a group consisting of steel,zirconium, titanium, Monel, Inconel, Hastelloy, Udimet 50, Stellite,Rene 41, and Rene
 88. 9. Apparatus as in claim 1 wherein the innerdiameter is between about two inches and about fifty inches.
 10. Anapparatus for crystal growth comprising: a cylindrical capsule regionfor containing a cylindrical capsule within which a crystal is to begrown under elevated pressure and temperature, the cylindrical capsuleregion having a length and ends; an annular heating member enclosing thelength of the cylindrical capsule region for heating the contents of thecylindrical capsule to an elevated temperature to create an elevatedpressure within the capsule; at least two stacked annular ceramic orcermet or metal members disposed around the annular heating member,wherein each of the at least two annular ceramic or cermet or metalmembers are made of a material having a compressive strength of about0.5 GPa and greater; and an enclosure disposed around all of the atleast two annular ceramic members.
 11. Apparatus as in claim 10 whereinthe annular heating member is substantially rigid.
 12. Apparatus as inclaim 10 wherein the annular heating member is disposed in contact withthe cylindrical capsule.
 13. Apparatus as in claim 10 wherein theannular heating member is disposed in contact with the at least twoannular ceramic or cermet or metal members.
 14. Apparatus as in claim 10further comprising a cylindrical sleeve surrounding each of the at leasttwo annular ceramic or cermet or metal members.
 15. Apparatus as inclaim 14 wherein the cylindrical sleeve applies compressive force to theat least two annular ceramic or cermet or metal members.
 16. Apparatusas in claim 14 wherein the cylindrical sleeve comprises a materialselected from steel, iron, nickel, and alloys thereof.
 17. Apparatus asin claim 10 wherein the enclosure comprises a material selected from agroup consisting of steel, zirconium, titanium, Monel, Inconel,Hastelloy, Udimet 500, Stellite, Rene 41, and Rene
 88. 18. Apparatus asin claim 10 wherein the inner diameter is between about two inches andabout fifty inches.
 19. A method of crystal growth comprising: providingan apparatus for crystal growth which includes: a cylindrical capsulewithin which a crystal is to be grown under elevated pressure andtemperature, the cylindrical capsule region having a length and ends; anannular heating member enclosing the length of the cylindrical capsulefor heating the contents of the cylindrical capsule to an elevatedtemperature to create an elevated pressure within the capsule; at leastone annular ceramic member disposed around the annular heating member,each of the at least one annular ceramic members comprising one or moreof a rare earth metal oxide, zirconium oxide, hafnium oxide, magnesiumoxide, calcium oxide, aluminum oxide, yttrium oxide, sialon (Si—Al—O—N),silicon nitride, silicon oxynitride, garnets, cristobalite, and mullite;and an enclosure disposed around all of the at least one annular ceramicmembers placing solvent in the capsule; heating the capsule using theheating member to cause an increase in temperature within the capsule togreater than 200 degrees Celsius to cause the solvent to be superheated;and slidably removing the capsule from the heating member aftercompleting the crystal growth.
 20. The method of claim 19 furthercomprising forming a crystalline material from the superheated solvent.